The present invention relates to a magnification varying device for use in a copying machine.
In general, a copying machine is used to produce copies which are equal in size to an original. Such a process is hereinafter referred to as "an equal magnification" or "lifesize" duplication or reproduction. However, for carrying, arranging in order or storing large documents such as newspapers or drawings, it is desirable that the copying machine be capable of producing copies which are scaled down from the original. In this respect, conversion magnification factors of 0.866, 0.816 and 0.707 have generally been employed as reduction factors, respectively, to scale down a size in the A column according to Japanese Industrial Standard to a size lower in the B column, for instance, from A3 to B4, or to scale down a size in the B column to a corresponding size in the A column, for instance, from B4 to A4, or to scale down a size in the A or B column to a smaller size in the same column, for instance, from A3 to A4, or from B3 to B4.
A mechanism for providing such size reduction has been described in the specification of Laid-Open Japanese Patent Application No. 65736/1978. However, such a mechanism is still disadvantageous in that it is intricate in construction and it must be manufactured with high accuracy with the result that it is high in manufacturing cost because the size reduction process is carried out by moving an image forming lens and mirrors in the system's scanning optical system.
Furthermore, a size reducing mechanism employing a zoom lens is known in the art. In general, the zooming mechanism of a zoom lens employs a aystem in which zooming is carried out using an elongated cam groove formed in the lens frame as a guide. Because of the groove, such a frame tends to be low in rigidity and is accordingly liable to be deformed. Thus, the use of a zooming mechanism involves difficulties. In addition, a zooming mechanism is necessarily bulky.
Especially in a copying machine using a zoom lens, the lens must be driven by an electric motor so that a stopper mechanism and a motor control device must be employed in combination to position the zoom lens at a desired position. Accordingly, a copying machine employing a zoom lens is unavoidably intricate and high in manufacturing cost.
Accordingly, an object of the present invention is to provide a variable magnification unit which has a low manufacturing cost but high accuracy in which all of the above-described difficulties have been eliminated.